As a system that wheels are driven by output of a rotary electric machine and a vehicle travels, there are a hybrid system of driving wheels on the basis of output of an engine or both engine and rotary electric machine and a system of driving wheels only by rotary electric machine. In either of the systems, the DC power is converted to AC power by the power converter and the AC power is supplied to the rotary electric machine for driving wheels. On the basis of the supplied power, the rotary electric machine generates rotating torque, and the wheels are driven by the rotating torque, thus the vehicle travels.
The rotary electric machine for driving wheels is required for large torque output, thus the power supplied to the rotary electric machine from the power converter is increased, and the internal heat of the power converter is apt to increase.
Further, an example relating to the cooling structure of the power converter for vehicle is disclosed in Japanese Patent Laid-open No. 2001-45601.